Recently, electro-mechanical elements such as micro-actuators are attracting attention. Such elements may realize very small and highly accurate component parts, and the productivity may be greatly improved by using a semiconductor process. Particularly, a micro-actuator using piezoelectric elements is now under development as a element for fine displacement of a scanning tunnel microscope and for fine positioning of a head slider of a magnetic disk recording and reproducing unit (hereinafter called a disk drive unit).
In a disk drive unit, a magnetic head for recording and reproducing information on a magnetic disk is mounted on a head slider and attached to an actuator arm. The actuator arm is driven by a voice coil motor (hereinafter called VCM) and positioned to the specified track position on the magnetic disk, thereby recording and reproducing information by the magnetic head. However, as the recording density is improved, it is now very difficult to assure sufficient accuracy in such a conventional method of positioning by VCM only. Accordingly, in addition to a positioning means by VCM, technical developments are now in progress to realize high-speed and highly accurate positioning by fine driving of a head slider with use of a fine positioning means using piezoelectric elements.
Including an actuator as mentioned above, piezoelectric elements are expected to be applied in various ways. To meet the expectation, piezoelectric elements are required to be small-sized, able to render low voltage drive possible and to generate considerable displacement, and a method of manufacturing thin film is now examined for the manufacture of such elements. In a thin film manufacturing method, piezoelectric elements are manufactured such that a piezoelectric thin film and electrode layer are first formed on a substrate such as a silicon mono-crystalline substrate and then processed for pattern forming, and finally, the piezoelectric element is separated from the substrate. However, since piezoelectric elements made by a thin film manufacturing method are very thin, after separating the piezoelectric elements from the substrate, it is very difficult to mount the piezoelectric elements on a mounting substrate without damaging them, and as a result, there arises a serious problem of productivity.
Taking the above matter into consideration, a manufacturing method in which pyroelectric elements and piezoelectric elements are mounted on a separately disposed electrode forming substrate with good mass-productivity is disclosed (Japanese Laid-open Patent No. H11-345833). In this disclosure, an element transfer jig is prepared, and elements formed on a temporary substrate are bonded in specified positions to the element transfer jig by using resin or double-sided adhesive tape, followed by selectively etching only the temporary substrate. Subsequently, the electrode disposed on the electrode forming substrate and the electrode of the element are bonded opposite to each other, for example by means of soldering. After that, the resin or adhesive tape used for bonding the element is dissolved and removed to separate the element from the element transfer jig, thereby forming pyroelectric elements or piezoelectric elements bonded in a specified shape on an electrode forming substrate.
However, in this method, the elements are individually separated by cutting them off every temporary substrate, and after that, they are bonded one by one onto the element transfer jig, and the temporary substrate is removed by etching. Therefore, when simultaneously bonding all the elements onto the electrode forming substrate, it is necessary to bond the elements onto the element transfer jig. However, since the elements are bonded one by one, it is relatively difficult to improve the accuracy.
Also, disclosed is a structure such that, after bonding pyroelectric thin film with organic thin film onto a substrate provided with an opening, the substrate with pyroelectric thin film formed thereon is removed by etching, thereby holding the pyroelectric thin film only by the organic thin film (Japanese Laid-open Patent No. H4-170077). In this method, after forming organic thin film so as to cover the pyroelectric thin film formed on a specified substrate, it is bonded onto a polyimide substrate provided with an opening. After that, the substrate with the pyroelectric thin film formed thereon is removed by etching, and at the opening portion, the pyroelectric thin film is held only by the organic thin film. Also in this manufacturing method, a substrate with pyroelectric thin film formed thereon is bonded onto a mounting substrate like a polyimide substrate, and after that, only the substrate is removed by etching. That is, since the substrate with pyroelectric thin film formed thereon is etched after mounting, the chemical solution or gas used for etching may cause the mounting substrate or the wiring electrode to change in quality or the shape of the mounting substrate is subjected to restrictions.
The present invention is intended to provide a thin film piezoelectric element and its manufacturing method, wherein the structure is such that thin film piezoelectric elements formed by a thin film manufacturing method are held by an element protective layer even after the element forming substrate is removed by etching, and that the mounting substrate is devised so as to prevent the element forming substrate from being exposed to the etching solution, and thereby, it is possible to improve the mass-productivity including the manufacturing process up to the mounting step and the reliability of the elements in a state of being mounted on a substrate.